For example, hydrometallurgy for nickel oxide ore includes a sulfuration process for forming a metal sulfide by injecting hydrogen sulfide gas to a solution obtained by neutralizing a leach liquor of nickel oxide ore or a nickel recovery solution from which impurities have been removed.
The hydrogen sulfide gas used here is produced by, for example, a hydrogen sulfide gas production plant having a structure as depicted in FIG. 5 or FIG. 6.
Specifically, a hydrogen sulfide gas production plant 50 depicted in FIG. 5 includes a reaction facility 51 for generating hydrogen sulfide gas from supplied sulfur and hydrogen gas, a cooling facility 52 for cooling the hydrogen sulfide gas, a washing facility 53 for washing the sulfur included in the hydrogen sulfide gas, and a drying facility 54 for drying the washed hydrogen sulfide gas to remove the moisture. The hydrogen sulfide gas production plant 50 further includes, as incidental facilities, a storing facility 55 for storing the generated hydrogen sulfide gas and a supplying facility 56 for supplying the hydrogen sulfide gas.
The hydrogen sulfide gas production plant 50 uses the catalyst in the reactor 51 for the purpose of reducing the activation energy. In the hydrogen sulfide gas production plant 50, after the sulfur included in the produced hydrogen sulfide gas is removed in the washing facility 53, the moisture is removed in the drying facility 54, whereby the corrosion of the facility due to the moisture is prevented.
In the hydrogen sulfide gas production plant 50, the pressure of the produced hydrogen sulfide gas is increased up to the necessary pressure by using the supplying facility 56 such as a compressor, and the hydrogen sulfide gas with the increased pressure is supplied to the plant where the hydrogen sulfide gas is used in the process of dezincification or sulfuration in the aforementioned hydrometallurgy for nickel oxide ore.
As for the condition of the hydrogen sulfide gas production plant 50 for producing the hydrogen sulfide gas, for example, the pressure is set to approximately 5 kPaG and the temperature is approximately 380° C. The operation is possible at low pressure and low temperature, which is advantageous because the catalyst is used in the reaction facility 51 in the hydrogen sulfide gas production plant 50.
In the hydrogen sulfide gas production plant 50, however, however, it is necessary to regularly exchange the catalyst in the reaction facility 51 and moreover to strictly manage the quality of the sulfur, which is the raw material of the hydrogen sulfide gas, from the viewpoint of the lifetime of the catalyst.
On the other hand, a hydrogen sulfide gas production plant 60 depicted in FIG. 6 is a plant where the catalyst is not used in the reactor. The hydrogen sulfide gas production plant 60 includes, as depicted in FIG. 6, a reaction facility (reactor 66, a quench tower 67, and a heater 68) 61 for generating the hydrogen sulfide gas from sulfur and hydrogen gas, cooling facilities 62 (62A, 62B) for cooling the hydrogen sulfide gas, a knockout facility 63 for removing the sulfur out of the hydrogen sulfide gas and supplying the hydrogen sulfide gas, and a blow-down facility 64 for recovering the sulfur removed from the hydrogen sulfide gas and supplying the sulfur to a sulfur processing plant or the like. In addition, the hydrogen sulfide gas production plant 60 includes, as an incidental facility, a facility 65 for decreasing the temperature of the sulfur in order to adjust the thermal balance.
In the hydrogen sulfide gas production plant 60, the molten sulfur is stored in the reactor 66 of the reaction facility 61 and by supplying the hydrogen gas from below, the reaction of the hydrogen sulfide gas progresses while the hydrogen gas passes through the molten sulfur. The decrease in sulfur by the reaction is compensated from above the reaction facility 61. The hydrogen sulfide gas generated in the reaction facility 61 is mostly hydrogen sulfide but also includes sulfur steam mixed when the hydrogen gas passes through the reactor.
Moreover, as for the condition of producing the hydrogen sulfide gas in the hydrogen sulfide gas production plant 60, for example, the pressure is as high as 800 kPaG and the temperature is as high as 470° C. The temperature of the generated hydrogen sulfide gas is as low as 150° C. when the gas exits from the quench tower 67 included in the reaction facility 61; moreover, the temperature thereof is decreased to approximately 50° C. (temperature used in the facility to which the gas is supplied) in the cooling facility 62 and then the gas is transferred to the knockout facility 63.
A large part of sulfur included in the hydrogen sulfide gas generated in the reaction facility 61 causes a trouble if firmly fixed to a measurement tool such as a thermometer or a pressure gauge or a valve such as a manual valve or a control valve of a plant in which the hydrogen sulfide gas is used and to which the sulfur is supplied. Therefore, the sulfur is solidified once in the knockout facility 63 and the sulfur deposited at the bottom is heated to be molten with steam through a jacket installed at the outer periphery of the bottom of the knockout facility 63 and thus the sulfur is recovered. The recovered sulfur is stored in the blow-down facility 64 and then supplied to the sulfur processing plant by using a supply pump 69 and processed therein or iteratively used therein.
In this manner, the sulfur included in the hydrogen sulfide gas generated in the hydrogen sulfide gas production plant 60 is separated in a knockout drum and the hydrogen sulfide gas is supplied to a plant where the hydrogen sulfide gas is used in the process of dezincification or sulfuration in the aforementioned hydrometallurgy for nickel oxide ore.
In the hydrogen sulfide gas production plant 60, the operation is managed with the pressure in the system set high; therefore, the facility such as the compressor or the chiller facility is not necessary to thereby suppress the initial investment. Moreover, the regular exchange of the catalyst and the cost required for the exchange, and the maintenance cost including the quality control of the sulfur, which are necessary in the hydrogen sulfide gas production plant 50 as described above, are not necessary, which is advantageous in terms of the operation cost.
In the hydrogen sulfide gas production plant 60, however, the operation is conducted at high pressure and high temperature; therefore, when the produced hydrogen sulfide gas is supplied, it is necessary to reduce the pressure to the appropriate pressure in the operation of the plant to which the gas is supplied. For example, in the plant in the sulfuration process for generating the mix sulfide (mix sulfide: MS) including nickel and cobalt by processing nickel oxide ore, the pressure of the hydrogen sulfide gas is set to approximately 350 kPaG; in the plant in the dezincification process for producing the zinc sulfide from zinc included in the neutralizing finish solution by performing the sulfuration, the pressure of the hydrogen sulfide gas is set to approximately 5 kPaG or less. In addition, the operation of the hydrogen sulfide gas production plant 60 is conducted at high pressure and high temperature; therefore, the risk in the occurrence of gas leak is high and the hydrogen sulfide gas cooling facility 62 as the facility for cooling the sulfur (sulfur steam) included in the hydrogen sulfide gas and the knockout facility 63 as the facility for recovering the hydrogen sulfide gas are heavily burdened.
In the hydrogen sulfide gas production plant 60, the sulfur included in the generated hydrogen sulfide gas is removed in the knockout facility 63 but part of the sulfur is solidified in the cooling facility 62 and fixed to the inside; if the solidified sulfur is left fixed thereto, the operation efficiency is deteriorated. Therefore, a plurality of cooling facilities is prepared and used alternately. Specifically, for example, two cooling facilities 62A and 62B are prepared and as the cooling performance is deteriorated by the sulfur fixed to the inside, the cooling facility 62A in use (facility with the sulfur fixed therein) is replaced by the standby cooling facility 62B (with the sulfur removed therefrom). Then, the sulfur fixed to the inside of the cooling facility 62A whose cooling performance has deteriorated is recovered by being molten with steam to make the cooling facility 62A standby. By repeating this operation, the deterioration in rate of operation of the hydrogen sulfide gas production plant 60 is prevented. The sulfur molten and recovered by the cooling facilities 62 (62A and 62B) is transferred to the blow-down facility 64 and processed therein similarly.
Incidentally, in the hydrogen sulfide gas production plant 60, the cooling facility 62 (for example, cooling facility 62A) switched for the process of melting the fixed sulfur is the facility that has been used to cool the hydrogen sulfide gas till just a while ago. Therefore, the high-pressure and high-concentration hydrogen sulfide gas is left in the cooling facility 62A. For this reason, before the sulfur fixed to the inner wall of the cooling facility 62A is melted and recovered, the pressure in the cooling facility 62A needs to be released.
The hydrogen sulfide gas generated when the pressure is released, however, becomes so-called waste hydrogen sulfide gas and is wasted. Moreover, this waste hydrogen sulfide gas is very toxic and it is not allowed to release the gas in the air as it is. Therefore, it is necessary to discharge the gas after processing the gas in a flare facility (facility for decreasing the toxicity by burning the toxic gas) or a detoxifying facility in which caustic soda or the like is used.
In the ease of processing the waste hydrogen sulfide gas in the flare facility, however, the hydrogen sulfide gas becomes SOx gas and adversely affects the environment though slightly. In the case of detoxifying the gas in the detoxifying facility, on the other hand, the neutralizer such as caustic soda is necessary and the cost of the neutralizer is added.
Patent Literature 1 discloses a method for recovering extra hydrogen sulfide gas discharged from a sulfur reactor in the sulfuration process of producing MS by processing nickel oxide ore, wherein the extra hydrogen sulfide gas is reused in the sulfuration reaction through a liquid obtained by having the caustic soda absorb the hydrogen sulfide gas (the liquid is in the form of hydrosulfide soda or sulfide soda). Moreover, Patent Literature 2 discloses a method for recovering the hydrogen sulfide gas vaporized in the dehydration process by absorbing the gas in an organic amide solvent outside the system of the dehydration process and reusing the recovered hydrogen sulfide in the polymerization reaction as a raw material of the alkali metal sulfide.
These methods, however, do not allow the hydrogen sulfide to be recovered as gas and require the recovery solvent such as the caustic soda or the organic amide.